Electric switch



Dec. 4 1923.

G. A. BURNHAM ELECTRIC SWITCH Filed April 28 1922 Patented Dec. 4, 1923.

UNITED STATES PATENT OFFICE.

GEORGE A.- BURNHAM, OF SAUGUS, MASSACHUSETTS, ASSIGNOPV'TO SEARS B. CONDIT,

OF BROOKLINE, MASSACHUSETTS.

ELECTRIC SXVITCH.

Application filed April 28, 1922. Serial No. 557,058.

T all whom it may concern:

Be it known that I, Gnonon A. BURNHAM,

a citizen of the United States, residing at Saugus, in the county oi"? Essex and btate of Massachusetts, have invented an Improvement in Electric Switches, of which the following is a specification.

This invention relates to oil immersed electric switches especially adapted to control direct current circuits.

Oil immersed electric switches are 11Tllversally used to control alternating current circuits and the circuit is interruptedunder oil or other equivalent fluid.

A direct current circuit cannot ordinarily be interrupted in oil for the reason that the arc will usually persist, regardless of the separation of the arcing members,.and gen erate such a volume of gas and vapor as to cause damage to the switch. Consequently,

it has been universal practice to control direct current circuits by air-break switches and interrupt the circuit in air.

For large volumes of direct current, the air-break switch includes a main currentcarrying member comprising a brush memher built up of a plurality of laminae, and current interrupting members comprising auxiliary contact or arcing members from which the arc is drawn and by which the direct current circuit is interrupted.

For high values of direct current, the brush member, while relatively massive, be comes heated, and the contact junctions between the brush member and the stationary switch studs or contact blocks, especially, become heated and oxidize; and the contact resistance at these points becomes increased, and increased heating results.

By reason of the oxidization of the contact surface, constant inspection and cleaning of the switch is necessary to maintain the switch in good working order.

An object of this invention is to provide a switch for direct current circuits wherein the main current carrying components are shielded or insulated from the oxidizing influence of the atmosphere.

In carrying out the invention, I prefer to immerse the main current carrying members in a non-oxidizing and preferably electri cally-insulating fluid by which said members are insulated and shielded from the oxidizing influence of the atmosphere. The main current-carrying members are not adapted to interrupt the direct current circuit, and I. provide auxiliary contact or arcing mcnr berg without the insulating fluid and disposed in and surrounded by the air to strike the arc and interrupt the direct current cir cuit. With this arrangen'ient, the direct current is carried under an insulating fluid and interrupted in air.

The figure represents diagrammatically a direct current electric switch embodying the invention.

As here shown, the direct current switch includes the switch frame 10 comprising a cover for the receptacle 11 which is. adapted to contain some insulating fluid, as oil, in which the main current carrying members of the switch are immersed and insulated from the oxidizing influence of the atmosphere. The main stationary switch members 12 and 13 are carried by the switch frame 10 and terminate in contact blocks 14 and 15 which are immersed beneath the fluid in the receptacle. The main movable switch or bridging member comprises the brush member 16 which is carried on the end of the switch rod 17 and immersed in the fluid in the receptacle. The brush member is adapted to contact with and bridge the contact blocks 14: and 15 and conduct direct current therebetween but it is not adapted to interrupt the direct current circuit. The circuit is adapted to be interrupted in the air and for this purpose, the stationary auxiliary switch contact or arcing members 18 and 19 are disposed above the receptacle and exposed to and surrounded by air and suitably supported in position. Said arcing members 18 and 19 are connected with the main switch members 12 and 13 by the con ductors 20 and 21 respectively. An auxiliary bridging member 22 may be carried by the switch rod 17 or otherwise arranged to be movable into and away from bridging relation with the arcing members 18 and 19. Said auxiliary bridging member 22 and areing members 18 and 19 are not adapted nor mally to carry any appreciable current; and the main switch members 12 and 13 and main brush member 16 are adapted normallyto carry substantially the entire direct current load.

The arcing members 18 and 19 and auxiliary bridging member 22, and main switch members 1.2 and 13 and main brush member 16, are so arranged that, in normal switch-closed position, the direct current is carried by the main brush member. When.

19 and the circuit-interrupting arc is drawn in air at the arcing members.

In closingthe switch, the circuit is first completed in air through the arcing members 18 and 19 and subsequently carried in the insulating fluid through the main brush member 16.

With this arrangement, it will be noted that the main current carrying components are immersed in an insulating fluid and thereby protected from the oxidizing eflect of the air, and the current is carried in the insulating fluid and interrupted in air.

I claim: V

1. A direct current electric switch having main current carrying components immersed in an insulating fluid, and arcing members disposed in and surrounded by air.

2. A direct current electric switch having main contact members, and a main bridging member immersed in an insulating fluid, and arcing members disposed in and surrounded by air.

3. A direct current electric switch having main circuit-control members immersed in an insulating fluid, and auxiliary circuitcontrol members arranged in shunt with said nave-iii main circuit-control members and disposed in and surrounded by air.

' 4:- A direct current electric switch having a receptacle adapted to contain an insulating fluid, main contact and bridging mom hers immersed in the fluid in said receptacle, and auxiliary contact members arranged in shunt with said main contact and bridging members and disposed in and surrounded by air.

5. A direct cur-rent electric switch having means disposed in an insulating medium to carry the current in shunt with the aforesaid means to interrupt the circuit in air.

6. An electric switch having a receptacle.

adapted to contain an insulating fluid, main contact and bridging members immersed in the fluid in said receptacle. arcing members disposed in and surrounded by air and con nected electrically with said main contact members, and means to interrupt the circuit through the switch at said arcing members.

7 Direct current switch apparatus comprising an oil immersed switch and an airbreak switch electrically connected in parallel, and operating means for said switches arranged to open the air break switch last.

8. Direct current switching apparatus comprising an oil immersed switch and an airbreak switch electrically connected in parallel, and operating means for said switches arranged to open the air break switch last and close it first.

9, Electrical switching apparatus comprising two switches electrically connected in parallel, one of said switches surrounded by air and said other switch shielded from the air, and operating means for said switches arranged to open the shielded switch first.

In testimony whereof, I have signed my name to this specification.

GEORGE A. BURNHAM. 

